The treatment and monitoring of water is a critical societal need. Approximately three percent (3%) of all electricity produced in the United States is consumed by wastewater treatment infrastructure. Of the electricity produced, approximately one and one-half percent (1.5%) is used in the actual treatment of wastewater. Some existing treatment paradigms include aerobic digestion and anaerobic digestion, however, these paradigms suffer from several drawbacks. For example, aerobic digestion is an energy intensive process and creates significant byproducts, such as bio-solids. In addition, anaerobic digestion cannot treat water to levels low enough for environmental release. These drawbacks keep the cost of wastewater treatment high, which thereby affects a range of industries and municipalities. Thus, there is a critical need for cheaper and more energy efficient wastewater treatment technologies.
Bio-electrochemical systems (BES) are capable of generating electricity or other value-added products from the oxidation and reduction of organic matter. BES consist of electrodes, such as anode and cathodes, both or individually coated in bio-films with the ability to transfer or accept electrons from electrodes. Electrodes may also be coated in noble medals to catalyze one of the reactions taking place. The electrodes can then be separated by an electrolyte which conveys ions between them (generally a membrane).
Electrodes, bio-films, electrolytes, and catalysts may or may not be enclosed in a casing. Each of these elements, which include the casing, can be connected to external circuits, control systems, or other reactors for use in combined systems. The geometrical configuration of the elements in a microbial fuel cell and their material definition can together be defined as the “architecture” of the system.
Over the years, a number of different BES architectures and components have been developed and tested for different uses. Two major categories of architectures are those that operate in batch mode versus flow-through (or plug flow) mode. In a batch-mode system, an oxidant is placed in a reactor in batches and is treated until some endpoint is reached before the next batch is treated. In flow-through mode, a continuous flow of material to be treated is provided into a reactor with a concurrent flow out of the reactor for a constant volume to be retained inside.
Flow through reactors include side-ways flow or upward flow, such as the upflow microbial fuel cell (UMFC) In a UMFC, an organic-laden medium is percolated upwards through a porous anode material (i.e. graphite granules). A number of electrode designs have also been used in UMFC designs. Original UMFC designs used in laboratory tests were not scalable due to the use of flat electrode surfaces, which provided low surface areas per volume of reactor. Therefore, high surface area materials were developed, called a “brush anode”, consisting of small-diameter graphite fibers linked to a central core (generally a non-corrosive metal such as titanium) that provides both high conductivity as well as resistance to fouling. Brush anodes have been made of carbon fibers (e.g. PANEX®33 160K) and cut to a set length and wound using an industrial brush manufacturing system into a twisted core consisting of two titanium wires. When placed in a reactor, the total surface area of typical brush electrodes per volume of reactor has been estimated to be as high as 9600 m2/m3. Reactors using these brushes have produced up to 2400 mW/m2 in a cube reactor with a defined acetate medium. However, these electrodes are expensive due to the materials used. In addition, the form itself, a wrapped brush, requires several steps to manufacture.
Therefore, a need exists to address the aforementioned drawbacks of the prior art.